The present invention relates generally to improving sound absorption in an automotive vehicle. More particularly, the invention relates to an automotive vehicle space frame system of that is coated over a portion of its surface with an expandable sound absorbing material, to improve the sound absorption characteristics of the automotive vehicle by the reduction of airborne noise propagating throughout the frame cavities.
For many years the transportation industry has been concerned with designing hollow structural or other members that do not transmit or amplify noise from one portion of the vehicle to another, while also not adding significantly to the weight of the vehicle. One such technique has been to employ baffle structures, within hollow cavities of the space frame construction, for effectively blocking sound waves traveling through the sheet metal cavities. For instance, one popular technique has employed a baffle substrate that is coated or edged with a thermally polymeric material, which upon heat activation expands and fills the space defined between the substrate and a wall of the member. While these prior art devices perform well and are advantageous in many circumstances, they often require that the baffle substrate be shaped according to a predetermined configuration, which is generally dictated by the structure of particular sheet metal surroundings. In turn, this requires the manufacture of particular tooling for producing the substrate, which adds potential cost and delay, particularly if changes to the vehicle structure are implemented during the design stages. Accordingly, there is need for a simple low cost system that permits consistent and reproducible noise absorption within the vehicle cavities, and which can be employed across a wide range of different sizes or shapes of cavities.
The present invention is directed to a sound absorption system, and particularly one for automotive vehicle space frame structures, such as (without limitation) vehicle roof-rails and pillar structures. The system generally employs a substrate that is coated, over at least a portion of its surface, with a sound absorbing medium, and particularly a heat activated resinous sound absorption material. In a particular preferred embodiment, the substrate is an inner wall of a metal, plastic or composite vehicle body member, and it is at least partially coated with a heat activated polymer, (e.g., a formable hot melt adhesive based polymer or an expandable structural foam, examples of which include olefinic polymers, vinyl polymers, thermoplastic rubber-containing polymers, epoxies, urethanes or the like).
In one embodiment the sound absorption medium is placed on or adjacent one or more inner walls defining a cavity within an automotive vehicle space frame, such as a vehicle roof rails, pillars, rockers or otherwise. The sound absorption medium is activated to accomplish transformation (e.g., expansion or flow) of the polymer within the cavity. The resulting structure includes a wall that is coated over at least a portion of its surface with the sound absorption medium pursuant to which anachonic chamber principles are employed for sound management.